1. Field of the Invention
The present invention relates to an imaging apparatus, an imaging method, and a program.
2. Description of the Related Art
In an imaging apparatus in related art using a solid image pickup device such as a CCD (Charge Coupled Device), the quantity of light (light exposure) input into the image pickup device is adjusted by an aperture or electronic shutter speed. That is, when a bright scene is imaged, adjustments are made to reduce the light exposure so that so-called “overexposure” should not occur by an output signal of the image pickup device being saturated. Conversely, in a dark scene, adjustments are made to increase the light exposure so that so-called “underexposure” should not occur.
However, when a scene of high contrast is imaged (for example, backlight imaging or indoor/outdoor simultaneous imaging), there arises an issue described below. Due to an insufficient dynamic range of the solid image pickup device to be used, a bright portion is saturated to cause “overexposure” and “underexposure” is caused in a dark portion in which light exposure is insufficient by adjustments of light exposure alone so that it is difficult to properly reproduce both of such portions.
In order to solve this issue, a method of using two different electronic shutter speeds within a field has been developed (see, for example, Japanese Patent Application Laid-Open No. 6-141229). According to this method, the electronic shutter speed is changed for each field to image information of a bright area and that of a dark area separately and each piece of the obtained information is combined into one image. As an application of the above method, an imaging apparatus (wide dynamic range camera) capable of picking up images in a wide dynamic range is known.
Two types of operating states of a wide dynamic range camera are generally known: a composite imaging mode in which wide dynamic range imaging is performed and a normal imaging mode in which wide dynamic range imaging is not performed. However, high contrast in images obtained from the composite imaging mode are frequently lost and it is known that if switched to the composite imaging mode in conditions (scene) of a small brightness difference, an unnatural image with reduced contrast of image is obtained. To improve such conditions, a method of automatically switching to the normal imaging mode in conditions of a small brightness difference and to the composite imaging mode in conditions of a great brightness difference has been developed (see, for example, Japanese Patent Application Laid-Open No. 2002-84449).
According to Japanese Patent Application Laid-Open No. 2002-84449, a brightness difference between a bright portion and a dark portion of a pickup image detected in normal imaging mode is used as a switching condition from the normal imaging mode to the composite imaging mode. Then, in order to reduce the brightness difference in composite imaging mode, an underexposure correction and an overexposure correction are made by auto exposure control of a long-time exposure image signal and a short-time exposure image signal to expand the dynamic range.